1. Field of the Invention
The present invention relates to an optical recording material using an ethylene derivative having at its 1- and 2-positions heterocyclic groups which are cyclizable by irradiation with light to form a cyclohexadiene ring and thereby to change the optical properties and other 1- and 2-positions connected to each other to form a ring. More particularly, the present invention relates to an optical recording material using a photochromic compound, which is useful as various recording or memory materials, photocopying materials, light controlling materials, photosensitive printing materials, laser beam sensitive materials, photoprinting or optical filters, masking materials, actinometers or display materials.
2. Discussion of the Background
Various compounds have been known which have photochromic properties (photon mode color changes) and which undergo coloring or discoloring when irradiated with light. Photochromic materials utilizing such properties have been proposed.
For instance, Japanese Unexamined Patent Publication No. 149812/1980 discloses a photochromic material having a spiropyrane compound of the following formula dispersed in a nitrocellulose resin: ##STR1## wherein R.sup.a is a hydrogen atom or a halogen atom, R.sup.b is an alkyl group, and R.sup.c is a hydrogen atom or an alkoxy group.
Further, Japanese Unexamined Patent Publication No. 28824/1975 discloses a photochromic photosensitive material having a spiropyrane compound of the following formula dispersed in a polymer compound having an alcoholic hydroxyl group: ##STR2## wherein each of R.sup.d and R.sup.e is a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group.
Furthermore, Japanese Examined Patent Publication No. 28892/1970 discloses a photochromic material containing a spironaphthooxazine compound of the formula: ##STR3## wherein R.sup.f is a hydrogen atom, a halogen atom, a cyano group or an alkyl or alkoxy group having from 1 to 8 carbon atoms.
Meantime, there has been active research in recent years concerning employment of such photochromic compounds as reversible optical recording materials. For this purpose, the following conditions are required to be satisfied.
(1) Sensitivity to a semiconductor laser beam PA0 (2) Non-destructive reading out property PA0 (3) Thermal stability of recorded information PA0 (4) Quick response PA0 (5) Durability against repeated operation
When a photochromic compound is used as an optical recording material, a particularly serious problem is that the thermal stability of recorded information under item (3) among the above requirements is not adequate and the recorded information written in by the photochemical reaction is unstable. Namely, in the case of conventional photochromic compounds, the colored state is usually thermally unstable and tends to return to the initial state in a few hours at room temperature. Thus, they have a drawback that the thermal stability of recorded information is inferior.
On the other hand, those having good thermal stability have a problem that they are usually inferior in durability under repeated operation. Therefore, the conventional photochromic compounds can hardly be regarded as having fully satisfactory properties as optical recording materials.